Re: Help with what I believe is a hardening issue

On Wed, 10 Nov 2004, ericawd wrote:

> The first question: Is it possible to get the gelatin too hot when sizing?
> I heat it in a microwave to the point that I am unable to put my finger in
> for more than a second. There is usually steam coming off the surface.
> Could this be related to my speckling problem and related to developing
> prints in scalding water?

I agree with Kate, odds are that's the problem. The books say do not let
it get above 140 degrees F or "the gelatin will break down" -- though why
that never happened before, who can say (maybe because it wasn't so
serious before?). Certainly every recipe for gelatin chiffon pie, or a
bombe, warns against getting the gelatin too hot. Test it once with a
photo thermometer to get the feel of it. But the microwave may be too hard
to measure & control in any event -- Once the gelatin is soaked and the
remaining water added, I heat it in a pot on the stove, stirring and
testing (by the finger method) frequently. I'd even guess that without the
stirring in the microwavve parts of the solution get even hotter (MW
doesn't heat evenly).

> In regard to the glyoxal, I have never used it before, so I have a couple of
> questions. The Formulary said to use in the ratio 15ml to 1 liter of water.
> Does any one have a different ratio? Do you use it after each coating? Is
> 10 minutes a good length of time?

As noted, I use 15 ml/liter also, but only give one coat of gelatin at the
start (tho I would only harden at the end even with two coats). I've never
hardened for longer than 5 minutes, so I can't answer for 10 minutes.

> BTW the reason I suspected the formaldehyde was information I got from:
> http://www.biotech.ufl.edu/EM/data/form.html
>
> It says:
> We have been doing some research about the shelf life of 37% Formaldehyde.
> There is no definitive age after which 37% Formaldehyde is no longer useful
> as a stock solution. Formaldehyde chemistry is moderately complex, but after
> discussions with other microscopists, manufacturers and reviewing pertinent
> texts, the following observations are applicable. Formaldehyde should be
> stored at room temperature, cold temperatures encourage the formation of
> trioxymethylene with a resulting white precipitate. Formaldehyde should be
> stored tightly sealed, since exposure to air encourages the oxidation of
> formaldehyde to formic acid (37% formaldehyde is usually shipped with 10-15%
> methanol to inhibit this change). Our recommendation is, if the 37%
> formaldehyde solution is clear, colorless and has no precipitate, and has
> been stored at room temperature in a tightly sealed bottle that has not been

CUT...

It seems that in theory anyway, maybe even in life, formaldehyde can go
off, tho I've never heard of it happening, and I would still suspect that
it's more likely to become degraded for scientific purposes than for our
uses... And for sure, manufacturers like to put that "one year" limitation
on stuff because it gets them off the hook if anything goes wrong -- and
makes you buy more product. For instance the Lacquer-Mat can says best
before one year... I used it over at least a 5-year period & never noticed
a difference... (tho I do notice a difference in milk and cottage cheese,
which definitely go bad after a year).

Judy
Received on Thu Nov 11 20:58:26 2004